1. Technical Field
The present invention relates to an ink jet recording aqueous pigment ink. More specifically, the invention relates to an ink jet recording aqueous pigment ink containing a self-dispersing pigment.
2. Related Art
Various techniques are applied in recording methods for forming images on a recording medium on the basis of image data signals. Among such techniques, the ink jet technique can efficiently use inks and accordingly reduce running costs because the ink jet technique can be used to form an image directly on a recording medium by ejecting ink onto only a desired image area. In addition, little noise is produced when the ink jet technique is used, and the ink jet technique is thus advantageous as a recording method.
Pigment inks that can be applied to various types of recording media and that are superior in waterfastness and light fastness are attracting attention as a type of ink for the ink jet technique. However, ink jet recording pigment inks have disadvantages in color reproduction range, print density, and reliability. Accordingly, in order to solve these disadvantages, ink jet recording aqueous pigment inks containing a self-dispersing pigment, which can disperse stably without using a dispersant, are being developed.
For example, JP-A-5-186704 discloses a self-dispersing carbon black whose surfaces have been modified so as to have a surface functional group by introducing the hydroxy group to the carbon black surfaces in a molar ratio of the hydroxy group to the quinone group of 10:1. JP-A-8-3498 discloses a method for producing a self-dispersing carbon black oxide powder surface-modified with active hydrogen. In this method, sodium hypochlorite is dropped into a mixture of an acid carbon black and water, and then the mixture is stirred at a temperature of 100 to 105° C. for 10 hours for demineralization and concentration. The resulting pigment dispersed liquid is treated with an acid, concentrated and dried to yield the self-dispersing carbon black powder surface-modified with active hydrogen.
Furthermore, JP-T-2000-513396 discloses a method for producing a surface-modified coloring pigment having a C6H4SO3−Na+ group. In this method, a sodium nitrite solution is added to a mixture of a coloring pigment and a sulfanilic acid to prepare a pigment slurry. Then, hydrochloric acid is added to and mixed with the slurry at 70° C., followed by drying.
However, since inks, in general, contain various types of constituents and additives, such as a surfactant, an organic solvent and resin particles, the dispersion stability of the self-dispersing pigment can be degraded in the ink, and consequently, the pigment aggregates and forms sediment disadvantageously.